This invention relates to an electronic device for the control of moving elements in text and/or image processing equipment comprising detecting means suitable for detecting intervals of space P corresponding to displacements of the moving element, timing means associated with the detecting means and suitable for linking an initial time and a determined time interval TP with each of the intervals of space P, and exciting means associated with the moving element for exciting the moving element at n instants of time inside the time interval TP.
More particularly, the invention relates to an electronic device for controlling the positioning and activation of a print-head of a dot matrix printer, of the ink jet type for example, or of a sensor in equipment for the scanning of text and/or images.
Dot printing, for example printing with ink jet printers, is effected by making a print-head translate transversally to a medium, generally paper, and selectively exciting a plurality of nozzles, placed orthogonally to the direction of movement of the head, for printing on the paper medium or the sheet through the emission of ink. The times at which to excite the nozzles of the head are calculated by taking as the reference in cyclical fashion an interval of space or step P which, in cases where the head is moved by a step motor, corresponds to one step of the motor and, where the head is controlled by an optical or magnetic encoder, corresponds to the minimum interval detected by the encoder.
To effect printing, see for example the European Patent Publication EP-A-0 664 221, each step P is divided into a plurality of elementary steps P/n and the excitation of the nozzles of the head is effected upon the completion of each elementary step P/n.
The elementary step P/n is calculated by taking as the reference the interval TP, corresponding to the time taken by the print-head to travel the step P, and dividing the interval TP by the number n.
In the known art, the excitation of the nozzles is performed at the time TP/n and subsequently at each successive elementary step P/n by repeatedly adding TP/n until the reference period TP is reached.
The number n of excitations of the print-head in the step P is strictly related to the printing resolution which is calculated in xe2x80x9cpoints per inchxe2x80x9d (ppi) and corresponds to the number of excitations of the print-head per unit length of one inch or, in metric terms, 25.4 mm; the step P is in actual fact a sub-multiple of the unit length and the division of the step P into elementary steps P/n therefore gives the printing resolution.
Naturally the printing resolution in some printers can be selected from a range of discrete values between a minimum and a maximum printing resolution, for example 600 ppi or 1200 ppi.
A first problem in the known art comes from the method of calculating the value TP/n corresponding to the elementary step P/n.
In actual fact, as the division of the value TP by the number n generally gives a value having an integral part ti and a decimal part tr corresponding to the remainder, the result is that, it being impossible in a binary system such as an electronic printer to take into account the time tr, the latter is neglected and only the value ti which corresponds to the integral part of TP/n is used to excite the print nozzles.
By neglecting the time tr, by adding instant by instant the value ti and by exciting the print nozzles in correspondence with the instants of time thus calculated, it occurs that the error due to tr continues to rise until a maximum of n times tr, a value which in some cases may even correspond to a few elementary printing steps P/n. From the practical viewpoint, and assuming that ti is approximated up or down to the theoretical value TP/n, dot printing is of varying intensity in correspondence with the extremities of each step P.
A further technical problem, linked to the previous one, consists of the fact that, as n and accordingly the corresponding printing resolution increase, the error due to tr also increases, with the result that the uniformity of printing, and therefore the printing quality, worsens, exactly under the conditions where it should be maximal when the printing resolution is maximal.
The object of this invention is to resolve the range of technical problems described above and which may be resumed as a lack of uniformity observed in particular in dot matrix printers, but which is also present in scanning equipment and, in general, in text and/or image processing equipment using a movable element to be positioned and activated with precision in an interval of space P.
This technical problem is solved by the electronic device for the control of moving elements in text and/or image processing equipment characterised by control means associated with the timing means and with the exciting means both for selectively adding to the initial time a plurality of numerical values each corresponding to each of the n instants and for controlling the exciting means by way of the plurality of numerical values.
In accordance with a further characteristic of this invention, a method is also described for the control of moving elements in text and/or image processing equipment characterised by the technique of associating with the initial time and the time interval TP, a plurality of numerical values predefined in relation with the number of the n instants such that the combination of the time interval TP with the plurality of numerical values guarantees that each of the n instants inside the time interval TP is calculated by adding absolute values to the initial time and not by incrementally adding n-times the integral part of TP/n.